The present invention relates to a controller for an internal combustion engine.
Recent internal combustion engines for vehicles include fuel vapor processing mechanisms. A fuel vapor processing mechanism collects fuel vapor, which is generated in a fuel tank, with a canister, and prevents the fuel vapor from being released into the atmosphere. To maintain the amount of fuel vapor collected in the canister below an upper limit, the fuel vapor processing mechanism desorbs fuel vapor from the canister and draws the desorbed fuel vapor into an intake passage via a purge passage when the engine is running. The fuel vapor is then burned in combustion chambers. This processing is referred to as “purging of fuel vapor”. The purging of fuel vapor restores the fuel vapor collection capability of the canister.
When purging is being performed, fuel injected from a fuel injection valve is drawn into the corresponding combustion chamber of the engine together with the fuel vapor desorbed from the canister. The fuel injection control executed during purging estimates the amount of fuel added by the purging and corrects the fuel injection amount of the fuel injection valve. This prevents the air-fuel ratio from being affected by purging.
A certain length of time is required from when the purging is started until when the purged fuel vapor reaches the combustion chambers defined in cylinders. The correction of the fuel injection amount must take into consideration such delay time of the fuel vapor. Japanese Laid-Open Patent Publication No. 11-62729 describes a controller that calculates a value compensating for the transfer delay based on the engine speed. The controller then uses the compensation value to calculate a fuel amount corresponding to the purged amount of fuel vapor, or the fuel amount required due to purging, and corrects the fuel injection amount.
Regulations regarding the amount of fuel vapor released into the atmosphere have become stricter. This has resulted in demands for canisters with higher fuel vapor collecting capabilities. To satisfy such demands, the amount of purged fuel vapor may be increased so that the canister promptly recovers its fuel vapor collecting capability.
When a larger amount of fuel vapor is purged, the purged amount of fuel vapor tends to differ from the corresponding fuel injection correction amount. This difference lowers the correction accuracy of the fuel injection amount and must thus be eliminated.
The controller of Japanese Laid-Open Patent Publication No. 11-62729 fails to consider the timing for correcting the fuel injection amount in accordance with the purged fuel vapor amount. Thus, the controller may fail to perform fuel injection correction in accordance with changes in the concentration of fuel vapor. For example, the controller may excessively decrease the fuel injection amount even though the concentration of fuel vapor in the intake passage is not that high. Also, the controller may excessively increase the fuel injection amount even though the concentration of fuel vapor in the intake passage is not that low.